Such a charging device is disclosed in Japanese Unexamined Patent Application Publication Nos. 11-352554, 2001-255573, and 2001-255575.
A configuration of a general charging device of a strobe apparatus will be described with reference to FIG. 5.
In the drawing, a field effect transistor Q1 is connected in series with a primary side coil P of an oscillation transformer T, and a switching operation and the like of the transistor Q1 are controlled by a control circuit 1. A main capacitor 2 is connected in parallel with a secondary side coil S of the oscillation transformer T via a diode D. A series circuit of a xenon tube 3 and an insulated gate bipolar transistor Q2 is connected in parallel with the main capacitor 2. R1 is a resistor for detecting current that flows in the primary side coil P of the oscillation transformer T, R2 is a resistor for detecting current that flows in the secondary side coil S of the oscillation transformer T, and 4 is a high-voltage trigger circuit for generating pulse voltage so as to activate the xenon tube 3.
A control circuit 1 for controlling charging and emitting operations of the strobe is designed as an application-specific integrated circuit and includes a driving circuit 5 and a discharge detection circuit 6. A configuration of the control circuit 1 will be described with reference to FIG. 6.
First, when the driving circuit 5 sends a gate signal to a gate of the transistor Q1, as shown in FIG. 6a, current flows from a battery to the primary side coil P of the oscillation transformer T, as shown in FIG. 6b. While monitoring a terminal voltage of the resistor R1, the driving circuit 5 inverts the gate signal to “L” level when current I1 of the primary side coil P reaches a peak current value IPK1. By this operation, an energy accumulated in the primary side coil P of the oscillation transformer T is discharged into the secondary side coil S of the oscillation transformer T, and the main capacitor 2 is charged with an output voltage of the secondary side coil S via the diode D.
The discharge detection circuit 6 detects that current I2 flowing from the terminal voltage of the resistor R2 to the secondary side coil S is lower than detection current Ith2 as shown in FIG. 6c and notifies the driving circuit 5 of the detection result.
In this case, the driving circuit 5 inverts the gate signal to “H” level. By repeating the procedure mentioned above, the main capacitor 2 is charged. In a case where the strobe is needed for photographing in the state where the main capacitor is fully charged, when the “H” level signal is output from a FSW terminal, the transistor Q2 is activated to ON state, and accordingly, the high-voltage trigger circuit 4 outputs a high voltage pulse of several kilo-volts, and thereby the xenon tube 3 is excited so as to emit light.